When this study was initiated in 1962, the objectives were disposed toward the development of Kentucky Rock Asphalt for use as a traffic-bound base and surface on rural roads near its source and toward redevelopment of the material for use as hot-mixed, hot-laid, skid-resistant surface course for higher echelon roads. Between July 1962 and August 1965, eight experimental, lean rock-asphalt bases were constructed and evaluated (1, 2, 3).

During the fall of 1965 a hot-mixed, enriched, rock-asphalt surfacing material was successfully produced through a conventional hot-mix plant and laid with a paver on a 8.4-mile section of Nolin Dam Road (KY 728) in Edmonson County. The construction and interim performance of this project has been reported previously (3). The hot-mix process consisted of crushed rock asphalt, containing approximately four percent indigenous bitumen, as the total cold-feed aggregate, heated to 250-300°F, and enriched with four to five percent asphalt cement. The mixture was then laid and compacted with conventional hot-mix paving equipment.

The success of the hot-mix surface on the Nolin Dam Road project renewed interest in rock asphalt for high-type surfacing and resurfacing. A series of eight resurfacing projects, totaling 92.9 miles in length, was let for the 1966 construction season. A Special Provision (dated March 1966, Appendix C) was prepared to govern this work. The developer, W. G. Reynolds and Associates, expanded their rock asphalt production operations during the spring of 1966. A company was formed under the name of Gripstop Corporation and a large capacity crushing plant was set up in the Indian Creek Rock Asphalt Quarry in Edmonson County. At the end of the 1966 construction season, three of the resurfacing projects were completed and two were partially completed. On the basis of the experience gained during the 1966 construction season, a revised Special Provision (dated March 1967, Appendix C) was prepared, and seven additional resurfacing projects--totaling 53.5 miles in length--were let to contract.

The major revisions in the Special Provision pertained to laying procedures. During 1966 it was found that the hot··mix rock asphalt became stiff and unworkable very quickly after placing. As a consequence, the material was difficult to hand work, and it was also difficult to grader lay the material as a leveling course. The first two projects under construction in 1966 used rock asphalt as the leveling course material. On one project (US 68, Christian County) constructed in 1966, Class I binder was used for the leveling course. Change orders were prepared for the other projects awarded in 1966 in order to use the usual hot-mix surfacing (Class I, Type A) for the leveling course. These change orders did not materially change the total cost of the contract. The contractors and the Department agreed upon a price per ton for the asphaltic concrete leveling course material. Sufficient quantities of the remaining contract materials were deducted to balance the cost of the leveling course.

The application rate of the hot-mix rock asphalt was set at 85 pounds per square yard for an estimated one inch of compacted thickness for those projects let to contract during 1966. The asphalt cement added to the mixture was set up as a separate pay item. For those projects let during 1967, the hot-mix rock asphalt application rate was set at 60 pounds per square yard, the asphalt cement was not set up as a separate pay item; and leveling course material (conventional hot-mix material) was provided.

Construction of all resurfacing projects has been completed. The Nolin Dam Road surfacing has been in service two full years, and several performance inspections have been made--some of which have been reported (3). The other 15 hot-mix surfacing projects have been in service for periods of 1-1/4 years to a few months. Two performance inspections have been made on the projects constructed during 1966 and 1967, and one inspection has been made on the most recent project (Butler County). The construction and performance of each project is presented in this report (Appendix A) in the order of the start of construction. Discussion of the Nolin Dam Road is presented in Appendix D.

A discussion of the Moutardier Boat Ramp Road is also given in Appendix D. This is one of the lean rock-asphalt base projects which was surfaced with conventional hot-mix bituminous concrete during 1966.

Report Date


Report Number

No. 258b

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The opinions, findings, and conclusions in this report are not necessarily those of the Department of Highways or the Bureau of Public Roads.